Robust indication of MAC level error correction

ABSTRACT

In digital communications that utilize a data packet format wherein each data packet includes a physical layer (PHY) component and a media access control layer (MAC) component, the media access control layer component can be selectively protected by forward error correction (FEC). The receiving end receives an indication as to whether FEC has been applied, and makes an FEC decision based (12-15) on this indication. The accuracy of the received-side FEC decision and the robustness of the FEC indication can be improved by: making the FEC decision based on the results of FEC decoding applied to a media access control layer header within the media access control layer component; providing an FEC indication bit in the physical layer component; and using a plurality of bits to encode the FEC indication in either the physical layer component or the media access control layer component.

[0001] This application claims the priority under 35 U.S.C. §119(e)(1)of copending U.S. provisional application No. 60/364,324 filed on Mar.14, 2002, and incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The invention relates generally to digital communications and,more particularly, to the application of error correction in digitalcommunications.

BACKGROUND OF THE INVENTION

[0003] Forward error correction (also referred to herein as FEC or errorcorrection) has been incorporated into many digital communicationsystems. For example, FEC is specified in the IEEE 802.11e draft. Inconventional practice, the Media Access Control (MAC) layer canselectively apply FEC to the Physical Layer Service Data Unit (PSDU).The PSDU includes the MAC header and the MAC payload. FIG. 1diagrammatically illustrates pertinent portions of a conventional 802.11communication apparatus that includes FEC capability. In the example ofFIG. 1, a selector 13 in the MAC layer has an input 14 which receivesthe data stream 11 that passes from the physical (PHY) layer to the MAClayer. For each PSDU in the data stream 11, the selector 13 determineswhether to send the PSDU to a data path 17 for regular MAC processing orto a data path 19 for MAC processing with FEC.

[0004] The decision of the selector 13 is determined by its controlinput 12, which is driven by the output of an FEC decision decoder 15.The FEC decision decoder 15 determines whether to use regular MACprocessing or FEC MAC processing based on the value of a predeterminedbit in the MAC header. Such use of a single bit to control the selectiondecision at 13 limits the accuracy of the decision at 13 to the biterror rate (BER) of the system, for example, a BER of 10⁻⁴ for IEEE802.11 systems. Even if FEC has been applied to a given packet, the FECdecision decoder 15 cannot take advantage of the improved BER providedby the FEC, and the accuracy of the decision at 13 remains limited tothe nominal BER of the system, for example, the aforementioned BER of10⁻⁴ associated with IEEE 802.11 systems.

[0005] It is therefore desirable to improve the accuracy of MAC-levelFEC decisions such as illustrated generally at 12-15 in FIG. 1, and toprovide a more robust indication of the use (or non-use) of FEC.

[0006] Various embodiments of the invention improve the accuracy of thereceive-side FEC decision and the robustness of the FEC indication by:making the FEC decision based on the results of FEC decoding applied tothe MAC header; providing an FEC indication bit in the PHY component ofthe packet; and using a plurality of bits to encode the FEC indicationin either the PHY component of the packet or the MAC component of thepacket.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 diagrammatically illustrates an example of an FECdecision-making arrangement in a conventional digital communicationapparatus.

[0008]FIG. 2 diagrammatically illustrates exemplary embodiments of anFEC decision-making apparatus according to the invention.

[0009]FIG. 3 illustrates conventional packet structures according toIEEE 802.11.

[0010]FIG. 4 illustrates an example of an FEC indication bit in thesignal field of the PHY header of an IEEE 802.11b packet according tothe invention.

[0011]FIG. 5 illustrates an FEC bit in the signal field of the PHYheader of an IEEE 802.11a packet according to the invention.

[0012]FIG. 6 illustrates an FEC indication bit in the service field ofthe PHY header of an IEEE 802.11b packet according to the invention.

[0013]FIG. 7 illustrates the use of an encoded plurality of bits toprovide the FEC indication in the service field of the PHY header of anIEEE 802.11a packet according to the invention.

[0014]FIG. 8 diagrammatically illustrates exemplary embodiments of anFEC decision-making apparatus which can decode FEC indication bits inthe PHY header according to the invention.

[0015]FIG. 9 diagrammatically illustrates exemplary embodiments of atransmit-side apparatus for encoding an FEC indication into the PHYheader according to the invention.

[0016]FIG. 10 illustrates the use of an encoded plurality of bits toprovide the FEC indication in the MAC header of an IEEE 802.11 packetaccording to the invention.

[0017]FIG. 11 diagrammatically illustrates exemplary embodiments of anFEC decision-making apparatus which can decode the multi-bit FECindication in the MAC header of FIG. 10 according to the invention.

[0018]FIG. 12 diagrammatically illustrates exemplary embodiments of atransmit-side apparatus according to the invention for encoding into theMAC header FEC indication bits such as illustrated in FIG. 10.

[0019]FIG. 13 diagrammatically illustrates pertinent portions ofexemplary embodiments of a digital communication apparatus according tothe invention.

DETAILED DESCRIPTION

[0020]FIG. 2 diagrammatically illustrates exemplary embodiments of anFEC decision-making apparatus according to the invention. In theapparatus of FIG. 2, the FEC decision decoder 21 is itself an FECdecoder, for example, a Reed-Solomon decoder. The FEC decoder appliesFEC decoding to the MAC header. If the FEC decoding process results in asuccessful decoding of the MAC header, then a corresponding indicationof success at 22 causes the selector (for example the selector 13 ofFIG. 1) to select the FEC (e.g., Reed-Solomon) processing path (see 19in FIG. 1). On the other hand, if the FEC decoder fails to successfullydecode the MAC header, then the corresponding failure indication at 22will cause the selector to select the regular processing path (see 17 inFIG. 1).

[0021]FIG. 3 illustrates the general format of data packets used inconventional IEEE 802.11 systems. As shown in FIG. 3, the packet has aPHY component including a PLCP (Physical Layer Convergence Protocol)preamble and a PLCP header (also referred to as the PHY header), and aMAC component including the MAC header and the MAC payload. The MACcomponent is also referred to as the Physical Layer Service Data Unit(PSDU). In IEEE 802.11b systems, a modulation shift occurs at the timeboundary between the PHY header and the MAC header. In IEEE 802.11asystems, a modulation shift occurs within the PHY header, specificallyat the time boundary between the signal field and the service field. Inboth 802.11a and 802.11b systems, data bits that are transmitted beforethe modulation shift can be recovered at the receiving end with greaterreliability than can data bits that are transmitted after the modulationshift.

[0022] Accordingly, the present invention recognizes that the robustnessof the transmitted FEC indication can be improved by transmitting theFEC indication before the modulation shift. For example, for an 802.11bapparatus, available bit 7 of the signal field of the PHY header can beused to provide the FEC indication, as shown in FIG. 4. As an examplefor an 802.11a apparatus, the reserved bit between the Rate and Lengthsub-fields of the signal field of the PHY header can be used for the FECindication bit, as shown in FIG. 5. FIG. 6 shows another example for802.11b systems, wherein reserved bit 5 (B5) of the service field of thePHY header is used for the FEC indication bit.

[0023] Other exemplary embodiments of the present invention increase therobustness of the FEC indication by using a plurality of bits to encodethe FEC indication. FIG. 7 illustrates an example of this technique foran 802.11a apparatus. As shown in FIG. 7, a plurality of reserved bitsin the service field of the PHY header can be used to encode the FECindication. As one specific example, 3 bits can be used to encode theFEC indication according to a repetition code, and the FEC decisiondecoder at the receiver can use a majority vote of the 3 bits to decidewhether or not FEC applies. Although the 802.11a service field of FIG. 7is transmitted after the aforementioned modulation shift, neverthelessthe availability of multiple service field bits to encode the FECindication permits an improvement in the robustness of the FECindication.

[0024]FIG. 8 diagrammatically illustrates exemplary embodiments of anFEC decision-making apparatus according to the invention. In variousembodiments, the different codings of the FEC indication illustrated inFIGS. 4, 5, 6 and 7 can be appropriately decoded by the FEC decisiondecoder of FIG. 8. Thus, in the examples given, the FEC decision decoderof FIG. 8 analyzes the PHY (PLCP) header and makes the FEC decision inthe PHY layer. This FEC decision is then passed to the MAC layer tocontrol the selection of regular or FEC processing (see also 13, 17 and19 of FIG. 1). The FEC decision decoder of FIG. 8 can, in variousexemplary embodiments: inspect bit 7 of the signal field of the 802.11bPHY header (see also FIG. 4); inspect the bit between the Rate andLength sub-fields of the signal field of the 802.11a PHY header (seealso FIG. 5); inspect bit 5 of the service field of the 802.11 b PHYheader (see also FIG. 6); and decode a plurality of bits which followthe scrambler initialization sub-field in the service field of the802.11a PHY header (see also FIG. 6).

[0025]FIG. 9 diagrammatically illustrates exemplary embodiments of atransmit-side apparatus for encoding the FEC indication into the PHY(PLCP) header. In various exemplary embodiments, the FEC decisionencoder of FIG. 9 can encode the FEC decision (as received from the MAClayer) to produce an encoded FEC indication in the PHY header inaccordance with any of FIGS. 4-7. In some embodiments, the FEC decisionencoder simply routes an FEC decision bit received from the MAC layerdirectly to a selected location in the PHY header.

[0026]FIG. 10 illustrates another example of using a plurality of bitsto encode the FEC indication for IEEE 802.11 systems. In the example ofFIG. 10, bit 15 of the Frame Control field of the MAC header and bit 9of the QoS Control field of the MAC header are used to encode the FECindication. For example, FEC processing could be indicated when bothbits are one, and regular MAC processing could be indicated when bothbits are zero. Also in the example of FIG. 10, the two FEC indicationbits are timewise separated from one another by more than 200 bitswithin the 256-bit-wide MAC header. Such a separation between the FECindication bits provides additional robustness with respect to bursterrors.

[0027]FIG. 11 diagrammatically illustrates further exemplary embodimentsof an FEC decision-making apparatus according to the invention. In someembodiments, the FEC decision decoder 100 is capable of decoding in theMAC layer the coded FEC indication illustrated in the MAC header of FIG.10. The result of this decoding operation controls the selector 13.

[0028]FIG. 12 diagrammatically illustrates exemplary embodiments of atransmit-side apparatus capable of encoding the FEC indication into theMAC header. In some embodiments, the FEC decision encoder can encode theFEC decision (received from a higher layer) to produce an encoded FECindication in the MAC header in the manner described above with respectto FIG. 10.

[0029] Although the multi-bit coding examples shown in FIGS. 7 and 10use 3 and 2 bits, respectively, other embodiments use more than 3 bitsfor coding the FEC indication. As used herein, coding (and coder) canrefer to encoding operations (and corresponding encoders), such as thosedescribed herein, and also to decoding operations (and correspondingdecoders), such as those described herein. Also, although specificexamples of coding schemes have been described above with respect toFIGS. 7 and 10, different coding schemes, for example, Hamming codes,can be utilized in other embodiments.

[0030] In some embodiments, FEC encoding and decoding of the MACcomponent is performed by the PHY layer instead of the MAC layer.

[0031]FIG. 13 diagrammatically illustrates pertinent portions ofexemplary embodiments of a digital communication transmitter, receiveror transceiver apparatus according to the invention. In FIG. 13, auser's communications application 131 is coupled to a packet processor133 for permitting transfer of communication information therebetween.For transmission operations, the packet processor 133 formats thecommunication data into packets (for example, 802.11a or 802.11bpackets), and forwards the packets to a communication interface 135. Thecommunication interface 135 can use conventional techniques to interfacethe packets received from the packet processor 133 with a communicationsmedium. In the example of FIG. 13, the communications medium is awireless communications link 137, with which the interface 135communicates via an antenna 138. In reception operations, the process isgenerally reversed, such that the communications interface 135 usesconventional techniques to interface the communications medium 137 tothe packet processor 133. The packet processor 133 receives packets fromthe communications interface 135 and, in response to the receivedpackets, produces corresponding communication information for thecommunications application 131.

[0032] As shown in FIG. 13, the packet processor can include an FECdecision encoder, an FEC decision decoder, or both, depending uponwhether the apparatus is a transmitter, a receiver or a transceiver,respectively. In various exemplary embodiments, the FEC decisionencoders and decoders can correspond to those described above withrespect to FIGS. 2 and 4-12. Other than the FEC decision encoders anddecoders, the packet processor 133 can utilize conventional techniquesto construct packets in response to the communication informationreceived from communications application 131, and can also useconventional techniques to deconstruct the packets received fromcommunication interface 135 to produce corresponding communicationinformation for the communication application 131.

[0033] Although exemplary embodiments of the invention are describedabove in detail, this does not limit the scope of the invention, whichcan be practiced in a variety of embodiments.

What is claimed is:
 1. A digital communication apparatus that utilizes adata packet format wherein each data packet includes a physical layercomponent and a media access control layer component, comprising: amedia access control layer portion for processing the media accesscontrol layer component; and a physical layer portion coupled to saidmedia access control layer portion for processing the physical layercomponent, said physical layer portion including an input for receivingdigital information associated with the physical layer component andindicative of whether the media access control layer component has beenselected to be protected by an error correction code, and said physicallayer portion including a coder coupled to said input for applying acoding operation to said digital information.
 2. The apparatus of claim1, wherein said coder is an encoder and said coding operation is anencoding operation that encodes said digital information into thephysical layer component.
 3. The apparatus of claim 2, wherein saiddigital information is a single bit and said encoding operationtransfers said single bit into the physical layer component.
 4. Theapparatus of claim 2, wherein said encoding operation encodes saiddigital information into a plurality of bits in the physical layercomponent.
 5. The apparatus of claim 4, wherein said encoding operationencodes said digital information into said plurality of bits accordingto a repetition code.
 6. The apparatus of claim 4, wherein said datapacket format is an IEEE 802.11a format, and wherein said encodingoperation encodes said digital information into a service field of aphysical layer header within the physical layer component.
 7. Theapparatus of claim 2, wherein said encoding operation encodes saiddigital information into a physical layer header within the physicallayer component.
 8. The apparatus of claim 7, wherein said data packetformat is an IEEE 802.11 format, and wherein said encoding operationencodes said digital information into a signal field of the physicallayer header.
 9. The apparatus of claim 1, wherein said digitalinformation is carried in the physical layer component, and wherein saidcoder is a decoder and said coding operation is a decoding operationthat decodes said digital information.
 10. The apparatus of claim 9,wherein said digital information is a single bit in the physical layercomponent, and wherein said decoding operation inspects said single bit.11. The apparatus of claim 9, wherein said digital information includesa plurality of bits in the physical layer component.
 12. The apparatusof claim 11, said data packet format is an IEEE 802.11a format, andwherein said plurality of digital bits are carried in a service field ofa physical layer header within the physical layer component.
 13. Theapparatus of claim 11, wherein said decoding operation takes a majorityvote of said plurality of bits.
 14. The apparatus of claim 9, whereinsaid digital information is carried in a physical layer header withinthe physical layer component.
 15. The apparatus of claim 14, whereinsaid data packet format is an IEEE 802.11 format, and wherein saiddigital information is carried in a signal field of the physical layerheader.
 16. The apparatus of claim 1, wherein said coder includes anoutput, and wherein one of said input and said output is connected tosaid media access control layer portion.
 17. A digital communicationapparatus that utilizes a data packet format wherein each data packetincludes a physical layer component and a media access control layercomponent, comprising: a physical layer portion for processing thephysical layer component; and a media access control layer portioncoupled to said physical layer portion for processing the media accesscontrol layer component, said media access control layer portionincluding an input for receiving digital information indicative ofwhether the media access control layer component has been selected to beprotected by an error correction code, and said media access controllayer portion including a coder coupled to said input for applying tosaid digital information a coding operation that utilizes a plurality ofbits.
 18. The apparatus of claim 17, wherein said coder is an encoderand said coding operation is an encoding operation that encodes saiddigital information into the media access control layer component. 19.The apparatus of claim 18, wherein said encoding operation encodes saiddigital information into a plurality of bits in a media access controllayer header within the media access control layer component, andwherein two of said bits are separated from one another within the mediaaccess control layer header by more than a majority of a bit width ofthe media access control layer header.
 20. The apparatus of claim 17,wherein said digital information is carried in the media access controllayer component, and wherein said coder is a decoder and said codingoperation is a decoding operation that decodes said digital information.21. The apparatus of claim 20, wherein said digital information includesa plurality of bits in a media access control layer header within themedia access control layer component, and wherein two of said bits areseparated from one another within the media access control layer headerby more than a majority of a bit width of the media access control layerheader.
 22. The apparatus of claim 17, wherein said data packet formatis an IEEE 802.11 format.
 23. A digital communication apparatus thatutilizes a data packet format wherein each data packet includes aphysical layer component and a media access control layer component,comprising: a physical layer portion for processing the physical layercomponent; and a media access control layer portion coupled to saidphysical layer portion for processing the media access control layercomponent, said media access control layer portion including an inputfor receiving a media access control layer header contained within themedia access control layer component, and said media access controllayer portion including a decoder coupled to said input for applying anerror correction decoding operation to the media access control layerheader, said decoder having an output for providing, based on a resultof said error correction decoding operation, an indication of whetherthe media access control layer component is protected by an errorcorrection code.
 24. The apparatus of claim 23, wherein said errorcorrection decoding operation uses said error correction code.
 25. Theapparatus of claim 24, wherein said decoder is a Reed-Solomon decoderand said error correction code is a Reed-Solomon code.
 26. A method ofdigital data communication, comprising: transferring digital data viadata packets that each include a physical layer component and a mediaaccess control layer component; and for each said data packet, using thephysical layer component to provide an indication of whether the mediaaccess control layer component has been selected to be protected by anerror correction code.
 27. The method of claim 26, wherein said usingstep includes encoding a digital indicator into the physical layercomponent.
 28. The method of claim 27, wherein said digital indicator isa single bit, and wherein said encoding step includes receiving saidsingle bit and transferring said single bit into the physical layercomponent.
 29. The method of claim 27, wherein said digital indicatorincludes a plurality of bits in the physical layer component.
 30. Themethod of claim 29, wherein said encoding step includes encoding saidplurality of bits according to a repetition code.
 31. The method ofclaim 29, wherein said data packets are IEEE 802.11a data packets, andwherein said encoding step includes providing said plurality of bits ina service field of a physical layer header within the physical layercomponent.
 32. The method of claim 27, wherein said data packets areIEEE 802.11 data packets, and wherein said encoding step includesencoding said digital indicator into a signal field of a physical layerheader within the physical layer component.
 33. The method of claim 26,wherein said using step includes decoding a digital indicator from thephysical layer component.
 34. The method of claim 33, wherein saiddigital indicator is a single bit in the physical layer component, andwherein said decoding step includes inspecting said single bit in thephysical layer component.
 35. The method of claim 33, wherein saiddigital indicator includes a plurality of bits in the physical layercomponent, and wherein said decoding step includes decoding saidplurality of bits.
 36. The method of claim 35, wherein saidlast-mentioned decoding step includes taking a majority vote of saidplurality of bits.
 37. The method of claim 35, wherein said data packetsare IEEE 802.11a data packets, and wherein said plurality of bits are ina service field of a physical layer header within the physical layercomponent.
 38. The method of claim 33, wherein said data packets areIEEE 802.11 data packets, and wherein said digital indicator is in asignal field of a physical layer header within the physical layercomponent.
 39. A method of digital data communication, comprisingtransferring digital data via data packets that each include a physicallayer component and a media access control layer component, and for eachsaid data packet, using a plurality of bits in the media access controllayer component to provide an indication of whether the media accesscontrol layer component has been selected to be protected by an errorcorrection code.
 40. The method of claim 39, wherein said using stepincludes decoding said plurality of bits to obtain said indication. 41.The method of claim 39, wherein said using step includes providing saidplurality of bits in a media access control layer header of the mediaaccess control layer component, and wherein two of said bits areseparated from one another within the media access control layer headerby more than a majority of a bit width of the media access control layerheader.
 42. The method of claim 39, wherein said using step includesencoding said indication into said plurality of bits in the media accesscontrol layer component.
 43. The method of claim 39, wherein said datapackets are IEEE 802.11 data packets.
 44. A method of digital datacommunication, comprising: transferring digital data via data packetsthat each include a physical layer component and a media access controllayer component; for each said data packet, applying an error correctiondecoding operation to a media access control layer header containedwithin the media access control layer component of the data packet; andfor each said data packet, and based on a result of the error correctiondecoding operation that has been applied to the media access controllayer header thereof, providing an indication of whether the mediaaccess control layer component of the data packet is protected by anerror correction code.
 45. The method of claim 44, wherein, for eachsaid data packet, the associated error correction decoding operationuses the associated error correction code.
 46. The method of claim 45,wherein said error correction code is a Reed-Solomon code.
 47. A digitalcommunication apparatus that utilizes a data packet format wherein eachdata packet includes a physical layer component and a media accesscontrol layer component, comprising: a media access control layerportion for processing the media access control layer component; aphysical layer portion coupled to said media access control layerportion for processing the physical layer component, said physical layerportion including an input for receiving digital information associatedwith the physical layer component and indicative of whether the mediaaccess control layer component has been selected to be protected by anerror correction code, and said physical layer portion including a codercoupled to said input for applying a coding operation to said digitalinformation; and said physical layer portion including a communicationinterface coupled to said coder for interfacing between said coder and acommunication medium.
 48. The apparatus of claim 47, wherein thecommunication medium includes a wireless communication link.
 49. Theapparatus of claim 47, provided as an IEEE 802.11 apparatus.
 50. Theapparatus of claim 47, wherein said coder is one of an encoder forapplying an encoding operation and a decoder for applying a decodingoperation, and wherein said communication interface is for interfacingbetween the communication medium and one of an input of said decoder andan output of said encoder.
 51. A digital communication apparatus thatutilizes a data packet format wherein each data packet includes aphysical layer component and a media access control layer component,comprising: a physical layer portion for processing the physical layercomponent; a media access control layer portion coupled to said physicallayer portion for processing the media access control layer component,said media access control layer portion including an input for receivingdigital information indicative of whether the media access control layercomponent has been selected to be protected by an error correction code,and said media access control layer portion including a coder coupled tosaid input for applying to said digital information a coding operationthat utilizes a plurality of bits; and said physical layer portionincluding a communication interface coupled to said coder forinterfacing between said coder and a communication medium.
 52. Theapparatus of claim 51, wherein the communication medium includes awireless communication link.
 53. The apparatus of claim 51, provided asan IEEE 802.11 apparatus.
 54. The apparatus of claim 51, wherein saidcoder is one of an encoder for applying an encoding operation and adecoder for applying a decoding operation, and wherein saidcommunication interface is for interfacing between the communicationmedium and one of an input of said decoder and an output of saidencoder.
 55. A digital communication apparatus that utilizes a datapacket format wherein each data packet includes a physical layercomponent and a media access control layer component, comprising: aphysical layer portion for processing the physical layer component; anda media access control layer portion coupled to said physical layerportion for processing the media access control layer component, saidmedia access control layer portion including an input for receiving amedia access control layer header contained within the media accesscontrol layer component, and said media access control layer portionincluding a decoder coupled to said input for applying an errorcorrection decoding operation to the media access control layer header,said decoder having an output for providing, based on a result of saiderror correction decoding operation, an indication of whether the mediaaccess control layer component is protected by an error correction code;and said physical layer portion including a communication interfacecoupled to said coder for interfacing between said decoder and acommunication medium.
 56. The apparatus of claim 55, wherein thecommunication medium includes a wireless communication link.
 57. Theapparatus of claim 55, provided as an IEEE 802.11 apparatus.